Strip, method for manufacturing the same, and method for manufacturing pneumatic tire

ABSTRACT

A strip of a thermoplastic elastomer to be wound spirally on a cylindrical drum for forming an inner liner for a tire having a shape close to a finished sectional shape is provided. The strip is formed of composite layers of (A) a first layer made of a styrene-isobutylene-styrene triblock copolymer and (B) a second layer containing at least one of a styrene-isoprene-styrene triblock copolymer and a styrene-isobutylene diblock copolymer. The strip further has a strip main body and ear portions arranged on opposite sides thereof. The strip main body has a thickness (T 1 ) of 0.05 mm to 1.0 mm. The ear portions have a thickness (T 2 ) thinner than the thickness (T 1 ) of the strip main body and a width (W 2 ) of 0.5 mm to 5.0 mm. This ribbon-shaped strip reduces unevenness of the surface of a sheet formed by the opposite ends of the strip when manufacturing an inner liner.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 37 C.F.R. §1.53(b) continuation of U.S.application Ser. No. 13/879,553 filed Apr. 15, 2013, which is the §371National Phase Application of PCT International Application No.PCT/JP2011/063935 field Jun. 17, 2011, which claims priority on JapanesePatent Application Nos. 2011-125168 filed Jun. 3, 2011 and 2010-248862filed Nov. 5, 2010. The entire contents of each of these applications ishereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a strip for an inner liner used for apneumatic tire, a method for manufacturing the strip, and a method formanufacturing a pneumatic tire including the strip.

BACKGROUND ART

In recent years, in response to strong social demands for low fuelconsumption of vehicles, weight reduction of tires has been sought.Among tire members, weight reduction and the like of an inner liner alsohave begun. The inner liner is disposed inwardly in a tire, and has afunction of reducing an amount of leakage of air from inside to outsideof the pneumatic tire.

Currently, a rubber composition for such an inner liner employs, forexample, a rubber blend mainly containing a butyl rubber. The rubberblend contains the butyl rubber by 70 mass % to 100 mass %, and anatural rubber by 30 mass % to 0 mass %. In this way, the tire isprovided with improved air permeability resistance. In addition tobutylene, the rubber blend mainly containing the butyl rubber containsisoprene by approximately 1 mass %, which acts with sulfur,vulcanization accelerator, and zinc white to achieve cross-linkingbetween rubber molecules. In the case of normal blend, theabove-described butyl-based rubber needs to have a thickness of 0.6 mmto 1.0 mm for a tire of a passenger car, and needs to have a thicknessof approximately 1.0 mm to 2.0 mm for a tire of a truck/bus. In order toachieve weight reduction of such tires, use of polymer, which is moreexcellent in air permeability resistance than the butyl-based rubber andcan provide an inner liner layer with a thinner thickness, has beenrequested.

Conventionally, in order to achieve weight reduction of a tire, it hasbeen proposed to use a film made of a material including thermoplasticresin, instead of the above-described rubber composition. However, whena tire is manufactured using an inner liner of thin thermoplastic resin,the inner liner partially becomes too thin due to pressure in avulcanization step, with the result that the finishing gauge of theinner liner in the resulting tire product becomes thinner than thedesigned gauge. In the thin portion of the inner liner thus finished, aphenomenon (open thread) in which a carcass cord looks to stand outtakes place, thus giving a user an impression of bad inner appearance.In addition, when the inner liner is thin, gas barrier property becomespartially bad to decrease tire internal pressure, with the result thatthe tire may burst in the worst case.

Meanwhile, during traveling with the tire, large shear strain acts on avicinity of a shoulder portion in the inner liner. When the materialincluding the thermoplastic resin is used as the inner liner, this shearstrain is likely to cause detachment at an adhesion interface betweenthe inner liner and the carcass ply, with the result that air leakagetakes place from the tire, disadvantageously.

In Patent Literature 1 (International Publication WO2008/029781), a tireis manufactured using a strip of film layer stack in which thermoplasticresin and thermoplastic elastomer are blended. With the film layerstack, gas barrier property and adhesive property can be improved,whereby bonding can be achieved between the ribbon-shaped strips.However, in this technique, gauge is constant in a non-vulcanized rawcover of film layer stack. Hence, when the gauge is thinned, a buttressportion or the like in the finished tire after vulcanization may becomethin.

Patent Literature 2 (Japanese Patent Laying-Open No. 2009-220460)discloses a method for manufacturing an inner liner material byextrusion molding a thermoplastic elastomer composition in which athermoplastic resin constitutes a sea component and a rubber constitutesan island component into a sheet shape through an extrusion mouthpiece,wherein the extrusion mouthpiece has a mouthpiece slit having a thickextrusion portion in cross section between the central part of the slitand each of opposite ends of the slit and has a ratio (%) of thicknessincrement Δt with respect to length Δ1 of a thickness changing portionin the slit longitudinal direction is set at 0.01 to 10%. With thisstructure, it is intended to obtain characteristics of enhanced effectof preventing air leakage and of unlikeliness to peel off.

However, the size of the extrusion die is difficult to change, whichimposes limits on the size of tires to be manufactured. Even if severaltypes of extrusion dies are prepared, it will take time for stagechanging at the time of size changing, which decreases productivity.

Patent Literature 3 (Japanese Patent Laying-Open No. 2000-254980)discloses sequentially winding a ribbon-shaped unvulcanized rubber stripon a cylindrical drum, thereby forming a rubber component into a contourclose to a desired finished sectional shape.

Conventionally, an inner liner used for a pneumatic tire is obtained ingeneral by continuously extrusion molding into a predetermined finishedsectional shape from a rubber extruder or the like. The finishedsectional shape is determined by a mouthpiece provided at a head part ofthe rubber extruder. In the conventional method for extrusion moldinginto a finished sectional shape, the sectional size of a rubbercomponent is large, so that a large size rubber extruder needs to beused. As a result, a production line cannot be reduced in size.Moreover, to solve problems of deteriorated productivity in smallquantity, large variety production and the like, various types ofmouthpieces should be prepared depending on the types of tire and thelike, and besides, exchanging and adjusting operations of the mouthpieceand the like are required every time the type of tire to be manufacturedis changed.

However, when forming a tire component by a ribbon-shaped rubber strip,workability is disadvantageous due to tackiness between rubbercompositions and the rubber component formed of the rubber strip deformsdisadvantageously during storage.

Patent Literature 4 (Japanese Patent Laying-Open No. 2010-058437)discloses a method for molding a sheet by extruding melted resin into asheet shape from a die, holding the extruded resin sheet between a dieroller and a nip roller, at least one of which has a projecting shapeformed thereon, to transfer the projecting shape to the sheet, forming acut groove therein, and cooling and hardening.

Patent Literature 5 (Japanese Patent Laying-Open No. 9-19987) disclosesa layer stack for improving adhesive property between an inner linerlayer and a rubber layer. By providing adhesion layers on the oppositesides of the inner liner layer, the adhesion layers come into contactwith each other at an overlapping portion of the inner liner layer andare bonded firmly by heating. Air pressure retainability is thusimproved. However, these adhesion layers for overlapping in the innerliner layer will come into contact with a bladder in a heated state in avulcanization step and will be stuck to the bladder disadvantageously.

CITATION LIST Patent Literature

PTL 1: International Publication WO2008/029781

PTL 2: Japanese Patent Laying-Open No. 2009-220460

PTL 3: Japanese Patent Laying-Open No. 2000-254980

PTL 4: Japanese Patent Laying-Open No. 2010-058437

PTL 5: Japanese Patent Laying-Open No. 9-19987

SUMMARY OF INVENTION Technical Problem

The present invention provides a ribbon-shaped strip used for an innerliner and a method of manufacturing the strip. In general, a strip has aflat rectangular cross sectional shape. Therefore, when overlapping aribbon-shaped strip of predetermined width to make a wider sheet,overlapping portions on the opposite ends of the strip becomes thick, sothat the surface of a finished sheet has unevenness. Therefore, a firstobject of the present invention is to equalize the thickness of an innerliner by providing ear portions for the ribbon-shaped strip.

A second object of the present invention is to reduce rolling resistanceby weight reduction through the use of a thermoplastic elastomer stripand further to prevent the inner liner from breaking or deforming byheat and pressure of a bladder in a vulcanization step, thereby avoidingcracks in the surface and/or air remaining inside.

A third object of the present invention is to improve adhesive propertybetween the inner liner and a carcass ply through the use of thethermoplastic elastomer strip and to reduce crack growth in connectionwith repeated flection deformation during traveling with the tire.

Solution to Problem

The present invention is a strip of a thermoplastic elastomer to bewound spirally on a cylindrical drum to form an inner liner for a tirehaving a shape close to a finished sectional shape. The strip is formedof composite layers of (A) a first layer made of astyrene-isobutylene-styrene triblock copolymer and (B) a second layercontaining at least one of a styrene-isoprene-styrene triblock copolymerand a styrene-isobutylene diblock copolymer. The strip further has astrip main body and ear portions arranged on opposite sides thereof. Thestrip main body has a thickness (T1) of 0.05 mm to 1.0 mm. The earportions have a thickness (T2) thinner than the thickness (T1) of thestrip main body and a width (W2) of 0.5 mm to 5.0 mm.

The strip preferably has a width (W0) of 5 mm to 40 mm. The ear portionsof the strip preferably have a thickness of 0.02 mm to 0.5 mm. The firstlayer has a thickness of 0.05 mm to 0.6 mm, and the second layer ispreferably adjusted to have a thickness of 0.01 mm to 0.3 mm.

The present invention relates to a method for manufacturing the stripmade of a thermoplastic elastomer, including the steps of (a) extrudingthe thermoplastic elastomer by an extruder having an extruder main bodyand an extrusion head to form a sheet having a horizontally longrectangular cross sectional shape, (b) passing the sheet through a pairof die rollers and transferring a shape of the die rollers on the sheetto form the strip having the ear portions on ends thereof, and (c)detaching the strip from the die rollers.

Furthermore, another aspect of the present invention relates to a methodfor manufacturing a pneumatic tire, characterized in that the strip iswound spirally on the cylindrical drum to form the inner liner, and theinner liner is disposed on an inner surface of a raw tire, and thenvulcanization is performed.

Advantageous Effects of Invention

According to the present invention, a ribbon-shaped strip of athermoplastic-elastomer material having ear portions on the oppositeends is used for an inner liner. An unvulcanized raw cover adjusted inthickness depending on the arrangement position in a tire can thus bedesigned. For example, merely a buttress portion can be designed to bethick, which can improve gas barrier property and tire durability.Moreover, because the strip is of ribbon shape, it is applicable totires of any tire size. Particularly because of the use of a layer stackof thermoplastic elastomers, the overall thickness can be made thin toachieve weight reduction while maintaining air shutoff property, so thatrolling resistance can be reduced. Furthermore, adhesive property withan adjacent carcass ply can be improved, so that flection crack growthcan be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross sectional view of the right half of apneumatic tire of the present invention.

FIG. 2 is a schematic view of a device manufacturing a strip of thepresent invention.

FIG. 3 is a cross sectional view showing the distance between a die rolland a nip roll in the manufacturing device shown in FIG. 2.

FIG. 4 is a schematic cross sectional view of a strip of the presentinvention.

FIG. 5 is a schematic cross sectional view of strips of the presentinvention.

FIG. 6 is a schematic cross sectional view of strips of the presentinvention.

FIG. 7 is a schematic view showing a method for manufacturing an innerliner using the strip of the present invention.

Each of FIG. 8(a) to FIG. 8(d) is a schematic cross sectional viewshowing an arrangement of an inner liner.

FIG. 9 is a schematic view showing a method for manufacturing an innerliner using a conventional strip

DESCRIPTION OF EMBODIMENTS Structure of Tire

The present invention relates to a method for manufacturing a pneumatictire including an inner liner disposed inwardly in the tire. The innerliner is manufactured by spirally winding a ribbon-shaped strip on acylindrical drum. The ribbon-shaped strip has ear portions on theopposite ends thereof. Here, the ribbon-shaped strip is manufactured byextrusion molding into a state close to a finished sectional shape.

The strip is formed of the polymer layer stack of at least two layers.The first layer is made of a styrene-isobutylene-styrene triblockcopolymer (SIBS), and has a thickness ranging from 0.05 mm to 0.6 mm.The second layer contains at least one of a styrene-isoprene-styrenetriblock copolymer (SIS) and a styrene-isobutylene diblock copolymer(SIB), and has a thickness of 0.01 mm to 0.3 mm. The second layer isarranged to be in contact with a rubber layer of a carcass ply.

An embodiment of a pneumatic tire manufactured by the present inventionwill be described based on the drawings. FIG. 1 is a schematic crosssectional view of the right half of the pneumatic tire. In the figure,pneumatic tire 1 includes a tread portion 2, and a sidewall portion 3and bead portions 4 so as to form a shape of toroid from the oppositeends of the tread portion. In each of bead portions 4, a bead core 5 isembedded. Further, a carcass ply 6 and a belt layer 7 are disposed.Carcass ply 6 is provided to extend from one bead portion 4 to the otherbead portion, and is anchored by winding its ends around bead cores 5.Belt layer 7, which is formed of at least two plies, is disposed outsidea crown portion of carcass ply 6.

Belt layer 7 is disposed such that two plies, which are formed of cordssuch as steel cords or aramid fibers, are arranged to allow the cords tocross each other between the plies normally at an angle of 5° to 30°relative to the tire circumferential direction. It should be noted thattopping rubber layers can be provided on the outer sides of the ends ofthe belt layer to reduce detachment in the ends of the belt layer.Further, in the carcass ply, organic fiber cords such as polyester,nylon, or aramid are arranged at substantially 90° relative to the tirecircumferential direction. In a region surrounded by the carcass ply andits turning portion, a bead apex 8 is disposed to extend from the upperend of bead core 5 in the sidewall direction. Further, an inner liner 9is disposed inwardly relative to carcass ply 6 in the direction of thetire radius, so as to extend from one bead portion 4 to the other beadportion 4.

Shape of Strip

Each of FIGS. 4 to 6 shows a cross sectional view of an embodiment of astrip 10. Strip 10 is configured such that a strip main body 10A has athickness (T1) of 0.05 mm to 1.0 mm and ear portions 10B formed on theopposite sides of strip main body 10A have a thickness (T2) thinner thanthe thickness (T1) of the strip main body. Ear portions 10B preferablyhave a width (W2) of 0.5 mm to 5.0 mm so as to smooth out unevennessthat would be formed on the surface wound on a drum. The strip has anoverall width (W0) adjusted to range from 5 mm to 40 mm, and preferablyranges from 10 to 30 mm.

In the present invention, the thickness (T1) of strip main body 10Aneeds to be in a range of 0.05 mm to 1.0 mm. If the thickness is lessthan 0.05 mm, extrusion molding will be difficult, and the number oftimes will be increased unnecessarily in order to form an inner liner ofpredetermined thickness. On the other hand, if the thickness exceeds 1.0mm, flection durability of the inner liner will be decreased and weightreduction can no longer be expected. The thickness (T1) of the strippreferably ranges from 0.1 mm to 0.5 mm.

The thickness (T2) of ear portions 10B, made thinner than the thickness(T1) of the strip main body, ranges from 0.02 mm to 0.5 mm, and morepreferably ranges from 0.05 mm to 0.2 mm. If the thickness (T2) of theear portions is thinner than 0.02 mm, extrusion dimensional accuracy maybe deteriorated. On the other hand, if the thickness (T2) of the earportions is thicker than 0.5 mm, unevenness of the surface formed byadjacent portions of the strip may be increased. Here, the thickness(T2) of the ear portions is defined as an average thickness in thewidthwise direction when it is changed in the widthwise direction of thestrip.

Moreover, the width (W2) of ear portions 10B is preferably adjusted torange from 0.8 mm to 3.0 mm, and the value of (W2×2) is preferably notmore than the value of (W0×0.5).

If width W2 of the ear portions falls outside the range of 0.5 mm to 5.0mm, the thickness dimension of the cross section of the inner linerformed by bonding the strip may become uneven.

Here, although ear portions 10B of the strip are preferably symmetric onthe right and left ends of the strip main body, they can be asymmetric.For example, in FIG. 4, the ear portion on the left end is formed with aconstant thickness on the lower surface, and the ear portion on theright end is formed with a constant thickness on the upper surface. Withsuch a shape, the ear portions of the strip adjacent to each other whenwinding the strip on the drum to form the inner liner reduce a stepdifference formed at the strip ends, enabling less uneven bonding. Itshould be noted that strip main body 10A has its thickness (T1) forminga horizontally-long, flat rectangular shape constant in the longitudinaldirection.

FIG. 5(a) shows a structure in which ear portions 10B of the strippartially have inclined sections. FIG. 5(b) shows an example in whichear portions 10B of the strip are formed only by inclined sections. Itshould be noted that, with the strip of the present invention, the earportions of the strip adjacent to each other when winding the strip onthe drum to form the inner liner can reduce a step difference at thestrip ends.

FIG. 6(a) shows ear portions 10B formed by forming steps on the rightand left ends of strip main body 10A, ear portions 10B being madethinner. Ear portions 10B have a constant thickness on the lower surfaceof the strip. In this case, when bonding the strip on the drum, a stepdifference will be formed at ends of adjacent portions of the strip, butthe unevenness can be reduced. FIG. 6(b) shows ear portions 10Bgradually decreasing in thickness toward the lower surface of the stripat the right and left ends of strip main body 10A. In this case, whenbonding the strip on the drum, a step difference will also be formed atends of adjacent portions of the strip, but an inner liner sheet havingless uneven surface shape can be obtained.

By forming the strip of the present invention into the above-describedshape, adjacent ear portions of the strip fit together appropriatelywhen winding the strip on the drum to form an inner liner, so that ajunction of even thickness can be formed. It should be noted that thethickness (T1) of strip main body 10A forms a horizontally long, flatrectangular shape constant in the longitudinal direction. It should benoted that not only these shapes but also various variations can beemployed for the ear portions of the present invention.

Method for Manufacturing Strip

A method for manufacturing strip 10 will be described with reference toFIG. 2. A strip manufacturing device 11 is composed of an extruder 13for extrusion molding of a thermoplastic elastomer sheet 12 having ahorizontally-long rectangular cross section and a pair of die rollers 14arranged in the vicinity of an extrusion port 16.

Extruder 13 includes an extruder main body 13A having a screw shaft 15and an extrusion head 13B forming a sheet of thermoplastic elastomerdischarged from this extruder main body 13A to extrude the sheet throughextrusion port 16. Extruder main body 13A kneads and melts the inputthermoplastic elastomer with screw shaft 15 driven by a motor having aslowdown function.

Extrusion head 13B has a mouthpiece 17 for extrusion molding attached tothe leading end of extruder main body 13A to constitute extrusion port16.

The pair of die rollers 14 has a structure having upper and lower rolls14A, 14B, and is held in the transverse direction orthogonal to thedirection of extrusion through extrusion port 16. Upper and lower dierolls 14A, 14B are rotatably drive controlled at the same speed and insynchronization with each other.

In addition, a gap between upper and lower die rolls 14A, 14B presents ashape resembling the sectional shape of strip 10, as shown in FIG. 3.Here, “resembling” refers to being substantially similar to thesectional shape of strip 10. The similarity proportion is usually in arange of 0.50 to 0.90 in consideration of expansion, and a gap K issmaller.

That is, one or both of upper and lower die rolls 14A, 14B are providedwith recessed sections 14 a, 14 b on the circumferential surface of astraight cylindrical roll body. Recessed sections 14 a, 14 b correspondto strip main body 10A. Therefore, ear portions 10B are molded by gapsK1 between die rolls 14A, 14B, and strip main body 10A is molded by agap K2 formed by recessed sections 14 a, 14 b.

In this way, in manufacturing device 11, horizontally-long rectangularsheet 12 is formed first by extruder 13, and the shape of the die rollis transferred to the sheet on the condition that heat is not generatedduring die roll molding. Then, strip 12A with the ear portions isdetached from die roller 14B by a free roller 18, and is processed intoa final shape. Accordingly, dimensional accuracy and stability areincreased, and manufacturing efficiency can be improved in that, forexample, a knife cutting operation for width adjustment usually requiredin calender molding becomes unnecessary. Besides, variations inthickness T2 of ear portions 10B can be reduced, so that strip 10 ofhigh quality can be manufactured.

It should be noted that, for that purpose, it is preferable to set anopening height HA1 of extrusion port 16 of extrusion head 13B at 2 to 7times thickness T1 of the strip and to set an opening width WA1 ofextrusion port 16 at 0.7 to 1.0 times width W0 of the strip.

If opening height HA1 exceeds 7 times T1 and opening width WA1 is lessthan 0.7 times W0, the processing ratio in die roll molding will beexcessively large, resulting in degraded quality and accuracy of strip10. Particularly, accuracy in width will become unstable, which willrequire width accuracy to be maintained by knife cutting. If openingheight HA1 is less than twice T1, the sheet thickness at the time ofextrusion will be thin in order to obtain strip 10 of not more than 1.0mm. Then, extrusion pressure will be higher, resulting in unstabledimensions. On the other hand, if opening width WA1 exceeds W0, theprocessing ratio will become too small to the contrary to cause strip 10to break, and dimensional stability will be deteriorated.

It should be noted that it is desirable to perform mold releaseprocessing on the die rolls and the free roll to be used in the moldingstep and the detaching step. Examples of a conventional technique thatcan be adopted for the mold release processing include a method forsubjecting the roll surface to nitriding (radical nitriding, Kanucprocess) to obtain a Cr—N coating (hardness Hv: 200 to 800; thickness:25 to 500 μm), plating obtained by impregnating hard chromium withTeflon® (hardness Hv: 800 to 1000; thickness: 25 to 1000 μm), adiamond-like carbon (DLC) coating (hardness Hv: 2000 to 7000; thickness:0.2 to 3.0 μm), and a Teflon® coating (hardness Hv: 100 to 500;thickness: 0.1 to 0.5 μm).

Polymer Layer Stack

In the present invention, the inner liner is manufactured by winding aribbon-shaped strip on the drum, and the strip is implemented by apolymer layer stack. Here, the polymer layer stack includes a firstlayer made of a styrene-isobutylene-styrene triblock copolymer (SIBS)and a second layer containing at least one of a styrene-isoprene-styrenetriblock copolymer (SIS) and a styrene-isobutylene diblock copolymer(SIB).

The first layer has a thickness of 0.05 mm to 0.6 mm. The second layeris adjusted to have a thickness not more than 0.4 mm, preferably 0.01 mmto 0.3 mm. The polymer layer stack is adjusted to have an overallthickness in a range of 0.05 mm to 1.0 mm, preferably in a range of 0.06mm to 0.9 mm.

By forming the strip with the ear portions by this polymer layer stackto manufacture an inner liner, surface unevenness can be reduced andmade smooth. This can solve the conventional problems, such as remainingair due to great unevenness.

First Layer

The first layer is made of the styrene-isobutylene-styrene triblockcopolymer (SIBS). An isobutylene block in the SIBS provides a polymerfilm made of the SIBS with excellent air permeability resistance.Therefore, when the polymer made of the SIBS is used for the innerliner, a pneumatic tire excellent in air permeability resistance can beobtained.

Further, the molecular structure of the SIBS is completely saturatedexcept aromatic side chain, so that the SIBS is restrained from beingdeteriorated and hardened and therefore has excellent durability.Therefore, when a polymer film made of the SIBS is used for the innerliner, a pneumatic tire with excellent durability can be obtained.

When manufacturing a pneumatic tire by applying such a polymer film madeof the SIBS to the inner liner, air permeability resistance can besecured. Therefore, it is not necessary to use a halogenated rubber,such as a halogenated butyl rubber, having been conventionally used toprovide air permeability resistance and having a high specific gravity.Even if it is used, an amount of usage thereof can be reduced.Accordingly, weight reduction of tire can be achieved, thus achievingthe effect of improving fuel efficiency.

The molecular weight of the SIBS is not particularly limited, but theSIBS preferably has a weight average molecular weight of 50,000 to400,000 measured through GPC measurement, in view of flowability,shaping step, rubber elasticity, and the like. When the weight averagemolecular weight thereof is less than 50,000, tensile strength andtensile elongation may be unfavorably decreased. On the other hand, whenthe weight average molecular weight thereof exceeds 400,000, extrusionworkability unfavorably becomes bad. In order to further improve airpermeability resistance and durability, the SIBS contains the styrenecomponent at a content of 10 mass % to 30 mass %, preferably, 14 mass %to 23 mass %.

In the copolymer of the SIBS, the isobutylene block preferably has adegree of polymerization in a range of approximately 10,000 to 150,000,and the styrene block preferably has a degree of polymerization in arange of approximately 5,000 to 30,000, in view of rubber elasticity andhandling (when the degree of polymerization is less than 10,000, eachblock will be in a liquid form).

The SIBS can be obtained through a general living cationicpolymerization method for a vinyl-based compound. For example, each ofJapanese Patent Laying-Open No. 62-48704 and Japanese Patent Laying-OpenNo. 64-62308 discloses that living cationic polymerization is possiblebetween isobutylene and another vinyl compound and use of isobutyleneand another compound for a vinyl compound allows for production of apolyisobutylene-based block copolymer.

The SIBS does not have a double bond other than an aromatic side chainin the molecule. Hence, the SIBS is stable to ultraviolet rays ascompared with a polymer having a double bond in molecule, such aspolybutadiene. Accordingly, the SIBS is excellent in weather resistance.Further, even though the SIBS does not have a double bond in themolecule and is a saturated rubbery polymer, the SIBS has a refractiveindex (nD) of 1.506 for light having a wavelength of 589 nm at 20° C.,as indicated by Polymer Handbook, Willy, 1989. This is significantlyhigher than that of another saturated rubbery polymer, such asethylene-butene copolymer.

The first layer made of such an SIBS has a thickness T1 of 0.05 mm to0.6 mm. If the thickness of the first layer is less than 0.05 mm, thefirst layer may be broken due to pressing pressure when vulcanizing theraw tire in which the polymer layer stack is applied to the inner liner,with the result that an air leakage phenomenon may take place in theresulting tire. On the other hand, if the thickness of the first layerexceeds 0.6 mm, the weight of the tire is increased to result indecreased performance in fuel efficiency. Further, the first layerpreferably has a thickness of 0.05 mm to 0.4 mm. The first layer can beobtained by forming the SIBS into the form of a film by means of ageneral method for forming thermoplastic resin or thermoplasticelastomer into a film, such as extrusion molding or calender molding.

Second Layer

The second layer contains at least one of the SIS layer made of astyrene-isoprene-styrene triblock copolymer (hereinafter, also referredto as “SIS”) and the SIB layer made of a styrene-isobutylene diblockcopolymer (hereinafter, also referred to as “SIB”).

The isoprene block of the styrene-isoprene-styrene triblock copolymer(SIS) is a soft segment. Hence, a polymer film made of the SIS is likelyto adhere to a rubber component through vulcanization. Therefore, when apolymer film made of the SIS is used for the inner liner, a pneumatictire excellent in durability can be obtained because the inner liner isexcellent in adhesive property with the rubber layer of the carcass ply,for example.

The molecular weight of the SIS is not particularly limited, but the SISpreferably has a weight average molecular weight of 100,000 to 290,000measured through GPC measurement, in view of rubber elasticity andmoldability. When the weight average molecular weight thereof is lessthan 100,000, tensile strength may be unfavorably decreased. On theother hand, when the weight average molecular weight thereof exceeds290,000, extrusion workability unfavorably becomes bad. The SISpreferably contains the styrene component at a content of 10 mass % to30 mass % in view of tackiness, adhesive property, and rubberelasticity.

In the present invention, it is preferable that in the SIS, the isopreneblock has a degree of polymerization in a range of approximately 500 to5,000 and the styrene block has a degree of polymerization in a range ofapproximately 50 to 1,500 in view of rubber elasticity and handling.

The SIS can be obtained through a general polymerization method for avinyl-based compound, such as the living cationic polymerization method.The SIS layer can be obtained by forming the SIS into the form of a filmby means of a general method for forming thermoplastic resin orthermoplastic elastomer into a film, such as extrusion molding orcalender molding.

The isobutylene block of the styrene-isobutylene diblock copolymer (SIB)is a soft segment. Hence, a polymer film made of the SIB is likely toadhere to a rubber component through vulcanization. Therefore, when apolymer film made of the SIB is used for the inner liner, a pneumatictire excellent in durability can be obtained because the inner liner isexcellent in adhesive property with an adjacent rubber forming thecarcass or an insulation, for example.

For the SIB, a linear SIB is preferably used in view of rubberelasticity and adhesive property. The molecular weight of the SIB is notparticularly limited, but the SIB preferably has a weight averagemolecular weight of 40,000 to 120,000 measured through GPC measurement,in view of rubber elasticity and moldability. When the weight averagemolecular weight thereof is less than 40,000, tensile strength may beunfavorably decreased. On the other hand, when the weight averagemolecular weight thereof exceeds 120,000, extrusion workabilityunfavorably becomes bad.

The SIB preferably contains the styrene component at a content of 10mass % to 35 mass %, in view of tackiness, adhesive property, and rubberelasticity.

In the present invention, it is preferable that in the SIB, theisobutylene block has a degree of polymerization in a range ofapproximately 300 to 3,000 and the styrene block has a degree ofpolymerization in a range of approximately 10 to 1,500 in view of rubberelasticity and handling.

The SIB can be obtained through a general polymerization method for avinyl-based compound, such as the living cationic polymerization method.For example, WO2005/033035 discloses a manufacturing method wherein theSIB is obtained by adding methylcyclohexane, n-butyl chloride, and cumylchloride into an agitator, cooling them to −70° C., reacting them for 2hours, then adding a large amount of methanol to stop the reaction, andperforming vacuum-drying at 60° C.

The SIB layer can be obtained by forming the SIB into the form of a filmthrough a general method for forming thermoplastic resin orthermoplastic elastomer into a film, such as extrusion molding orcalender molding.

Thickness T2 of the second layer is not more than 0.4 mm, and preferablyranges from 0.01 mm to 0.3 mm. Here, the thickness of the second layerrefers to the thickness of the SIS layer if the second layer is composedonly of the SIS layer, refers to the thickness of the SIB layer if thesecond layer is composed only of the SIB layer, and refers to the totalthickness of the SIS layer and the SIB layer if the second layer iscomposed of two layers of the SIS layer and the SIB layer. If thethickness of the second layer is less than 0.01 mm, the second layer maybe broken due to pressing pressure when vulcanizing the raw tire inwhich the polymer layer stack is applied to the inner liner, with theresult that vulcanization adhesion strength may be decreased. On theother hand, if the thickness of the second layer exceeds 0.4 mm, theweight of the tire is increased to result in decreased performance infuel efficiency. Further, the second layer preferably has a thickness of0.01 mm to 0.3 mm.

Manufacturing of Inner Liner

The strip of the present invention is formed by winding ribbon-shapedstrip 10. As shown in FIG. 7(a), strip 10 is sequentially wound spirallyon a cylindrical drum D, and adjacent portions of strip 10 formoverlapping portions to form an inner liner. Here, adjacent portions ofstrip 10 form a step difference during winding as shown in FIG. 7(b)with their ends shown on an enlarged scale, but the ear portions willreduce an uneven step difference d. On the other hand, as shown in FIG.9, an uneven step difference d0 formed in the case of using aconventional strip of rectangular cross section having no ear portionsis about twice the unevenness in the case of the strip having the earportions.

In this way, the use of the strip having the ear portions facilitatesmaking the inner liner resemble a finished sectional shape required ofthe inner liner. In addition, a smooth contour can be obtained, andsurface cracks can be prevented from occurring after vulcanization. Onthe other hand, the inner liner can be formed by approximately the samenumber of times of winding as in the case of a conventional strip of thesame thickness, which can restrain production efficiency from beingdeteriorated and air from remaining.

Method for Manufacturing Pneumatic Tire

The pneumatic tire of the present invention can be manufactured using ageneral manufacturing method. Polymer layer stack PL is used tomanufacture a strip. Then, the above-described method is used tomanufacture the inner liner. Pneumatic tire 1 can be manufactured byapplying the above-described inner liner to the raw tire of pneumatictire 1 and vulcanizing and molding them together with other members.When disposing polymer layer stack PL on the raw tire, the second layerof polymer layer stack PL, i.e., an SIS layer PL2 or an SIB layer PL3 isdisposed outwardly in the direction of the tire radius in contact withcarcass ply 61. With this arrangement, in the tire vulcanization step,adhesive strength can be increased between carcass 6 and SIS layer PL2or SIB layer PL3. In the resulting pneumatic tire, the inner liner andthe rubber layer of carcass ply 61 are adhered to each other in anexcellent manner. Thus, the pneumatic tire can have excellent airpermeability resistance and durability.

Arrangement of Inner Liner

FIG. 8 shows an arrangement of the inner liner formed of the polymerlayer stack in the vulcanized tire of the present invention. In FIG.8(a), a polymer layer stack PL is formed of an SIBS layer PL1 serving asthe first layer, and SIS layer PL2 serving as the second layer. Whenapplying polymer layer stack PL to the inner liner of the pneumatic tireand disposing SIS layer PL2 outwardly in direction of the tire radius soas to bring SIS layer PL2 into contact with carcass ply 61, adhesivestrength between SIS layer PL2 and carcass 61 can be increased in thestep of vulcanizing the tire. Accordingly, in the resulting pneumatictire, the inner liner and the rubber layer of carcass ply 61 are adheredto each other in an excellent manner. Thus, the pneumatic tire can haveexcellent air permeability resistance and durability.

In FIG. 8(b), polymer layer stack PL is formed of SIBS layer PL1 servingas the first layer, and SIB layer PL3 serving as the second layer. Whenapplying polymer layer stack PL to the inner liner of the pneumatic tireand disposing a surface of SIB layer PL3 outwardly in direction of thetire radius so as to bring the surface of SIB layer PL3 into contactwith carcass ply 61, adhesive strength between SIB layer PL3 and carcass61 can be increased in the step of vulcanizing the tire. Accordingly, inthe resulting pneumatic tire, the inner liner and the rubber layer ofcarcass ply 61 are adhered to each other in an excellent manner. Thus,the pneumatic tire can have excellent air permeability resistance anddurability.

In FIG. 8(c), polymer layer stack PL is formed of SIBS layer PL1 servingas the first layer, SIS layer PL2 and SIB layer PL3 both serving as thesecond layer. SIBS layer PL1, SIS layer PL2, and SIB layer PL3 arestacked on one another in this order. When applying polymer layer stackPL to the inner liner of the pneumatic tire and disposing a surface ofSIB layer PL3 outwardly in direction of the tire radius so as to bringthe surface of SIB layer PL3 into contact with carcass ply 61, adhesivestrength between SIB layer PL3 and carcass ply 61 can be increased inthe step of vulcanizing the tire. Accordingly, in the resultingpneumatic tire, the inner liner and the rubber layer of carcass ply 61are adhered to each other in an excellent manner. Thus, the pneumatictire can have excellent air permeability resistance and durability.

In FIG. 8(d), polymer layer stack 10 is formed of SIBS layer PL1 servingas the first layer, and SIB layer PL3 and SIS layer PL2 both serving asthe second layer. SIBS layer PL1, SIB layer PL3, and SIS layer PL2 arestacked on one another in this order. When applying polymer layer stackPL to the inner liner of the pneumatic tire and disposing a surface ofSIS layer PL2 outwardly in direction of the tire radius so as to bringthe surface of SIS layer PL2 into contact with carcass ply 61, adhesivestrength between SIS layer PL2 and carcass ply 61 can be increased inthe step of vulcanizing the tire. Accordingly, the inner liner and therubber layer of carcass ply 61 are adhered to each other in an excellentmanner. Thus, the pneumatic tire can have excellent air permeabilityresistance and durability.

EXAMPLES Material of Strip

The following thermoplastic elastomers (SIB, SIBS, and SIS) were usedfor manufacturing of the strip of the present invention.

SIB

Into a 2 L reaction container having an agitator, 589 mL ofmethylcyclohexane (dried with molecular sieves), 613 ml of n-butylchloride (dried with molecular sieves), and 0.550 g of cumyl chloridewere added. The reaction container was cooled to −70° C., and then 0.35mL of α-picoline (2-methylpyridine) and 179 mL of isobutylene wereadded. Further, 9.4 mL of titanium tetrachloride was added to startpolymerization. They were reacted with each other for 2.0 hours whilestirring the solution at −70° C. Next, 59 mL of styrene was added to thereaction container, and reaction was continued for another 60 minutes.Thereafter, a large amount of methanol was added to stop the reaction.After removing a solvent and the like from the reaction solution, thepolymer was dissolved with toluene and rinsed twice. This toluenesolution was added to a methanol mixture to precipitate a polymer. Thepolymer thus obtained was dried at 60° C. for 24 hours, therebyobtaining a styrene-isobutylene diblock copolymer.

The content of the styrene component: 15 mass %

Weight average molecular weight: 70,000

SIBS

“SIBSTAR 102 (Shore A hardness: 25; the content of the styrenecomponent: 25 mass %; weight average molecular weight: 100,000)”provided by Kaneka Corporation was used.

SIS

D1161JP (the content of the styrene component: 15 mass %; weight averagemolecular weight: 150,000) provided by Kraton Polymers was used.

Method for Manufacturing Inner Liner

Commercially available pellets were used for the above-described SIBSand SIS, and the SIB obtained by the above-described manufacturingmethod was used. They were mixed by the following formulation. Thismixture was extruded into a ribbon-shaped sheet (thickness: 0.3 mm) at ascrew speed of 80 RPM and an extrusion rate of about 9 m/min using anextruder shown in FIGS. 2 and 3 (screw diameter: 4180 mm; L/D: 50; diegap width: 40 mm; cylinder temperature: 220° C.).

This sheet was passed through die rolls 14A, 14B to manufacture strip12A with the ear portions of predetermined shape formed on the oppositeends. It should be noted that ribbon-shaped sheet 12 has a multilayerstructure obtained by coextruding thermoplastic elastomers of the firstlayer and the second layer using the above-mentioned extruder. Then, thestrip was passed by a free roller 19 and detached from the die rollersto obtain strip 12A having a sectional structure shown in FIG. 4. Here,strip 10 has width W0 of 20 mm and thickness T1 of 3 mm. Ear portions10B have width W2 of 0.3 mm and thickness T2 of 0.02 mm.

The above-described strip was wound on the drum shown in FIG. 7 andmolded into a wide sheet with adjacent ear portions of the strip formingjunctions together to manufacture a 0.3-mm-thick sheet for inner liner.

Formulation of Strip Thermoplastic elastomer (Note 1) 100 parts by massStearic acid (Note 2)  3 parts by mass Zinc oxide (Note 3)  5 parts bymass Antioxidant (Note 4)  1 part by mass Vulcanization accelerator(Note 5)  1 part by mass Sulfur (Note 6)  0.5 part by mass (Note 1)SIBS, SIS, and SIB were used for thermoplastic elastomers. (Note 2)Stearic acid: “Stearic Acid LUNAC S30” provided by Kao Corp. (Note 3)Zinc oxide: “Zinc White No. 1” provided by Mitsui Mining and SmeltingCo., Ltd. (Note 4) Antioxidant: “NOCRAC 6C”(N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) provided by OuchiShinko Chemical (Note 5) Vulcanization accelerator: “NOCCELER DM”(di-2-benzothiazolyldisulfide) provided by Ouchi Shinko Chemical (Note6) Sulfur: “Sulfur Powder” provided by TSURUMI CHEMICAL INDUSTRIES CO.LTD.

Manufacturing of Tire

A pneumatic tire of tire size of 195/65R15 was prototyped using an innerliner obtained by molding a strip based on the specifications shown inTable 1 on a drum. It should be noted that press vulcanization wasperformed for 20 minutes at 170° C. Then, the tire was cooled for 3minutes at 100° C. without removing the tire from the vulcanizationmold, and then was removed from the vulcanization mold.

It should be noted that the Examples were strips provided with earportions, and the Comparative Example was a strip having no earportions.

TABLE 1 Comparative Example 1 Example 1 Example 2 Example 3 Example 4Strip Shape Rectangular FIG. 6(a) FIG. 5(b) FIG. 4 FIG. 6(b) Width (WO)(mm) 20 20 40 40 10 Thickness (T1) (mm) 0.3 0.3 0.6 1.0 0.05 Width ofEar Portion (W2) (mm) — 3.0 5.0 5.0 0.5 Thickness of Ear Portion (mm) —0.02 0.3 0.5 0.02 (T2) Layer Stack First Layer: SIBS SIBS SIBS SIBS SIBSSIBS Thickness (mm) 0.25 0.25 0.4 0.6 0.04 Second Layer: SIS SIS SIS SISSIS SIS Thickness (mm) 0.05 0.05 0.1 0.2 0.01 Second Layer: SIB — — SIBSIB — Thickness (mm) 0.1 0.2 Tire Air-in C A A A A Performance FlectionCrack Growth C (88 cracks) A (0 crack) A A A Rolling Resistance Index100 103 104 102 105 Static Air Pressure Decrease 2.7%/M 1.8%/M 1.7%/M1.5%/M 1.8%/M

Method for Evaluating Tire Performance

For the pneumatic tires of the Examples and the Comparative Exampleshown in Table 1, performance evaluation was conducted by the followingmethods.

Air-In Performance

The inside of a vulcanized tire was checked by appearance and evaluatedas follows:

A: In appearance, per tire, the number of air bubbles with a diameternot more than 5 mm was 0, and the number of air bubbles with a diameterexceeding 5 mm was 0.

B: In appearance, per tire, the number of air bubbles with a diameternot more than 5 mm was 1 to 3, and the number of air bubbles with adiameter exceeding 5 mm was 0.

C: In appearance, per tire, the number of air bubbles with a diameternot more than 5 mm was 4 or more, and the number of air bubbles with adiameter exceeding 5 mm was 1 or more.

Flection Crack Growth Test

In endurance traveling test, evaluation was made depending on whetherthe inner liner was cracked or detached. Each trial tire was assembledto a JIS specification rim 15×6JJ. The tire internal pressure was set at150 KPa, which was lower internal pressure than normal internalpressure. The load was set at 600 kg. The speed was set at 100 km/h. Thetravel distance was set at 20,000 km. Inside of the tire was observed tomeasure the number of cracks and detachments. Evaluation was made on adetermination criterion that a tire with 50 or more cracks was rated C,a tire with 1 to 49 cracks was rated B, and a tire with 0 crack wasrated A.

Rolling Resistance Index

Each trial tire was assembled to a JIS specification rim 15×6JJ, and arolling resistance tester provided by Kobe Steel Ltd was used to measurerolling resistance thereof while performing traveling at a roomtemperature (30° C.) under conditions of a load of 3.4 kN, an airpressure of 230 kPa, and a speed of 80 km/h. Based on thebelow-described formula, the rolling resistance change ratio (%) of eachExample was expressed in an index with Comparative Example 1 being 100as a reference. As the rolling resistance change ratio is larger, therolling resistance is further reduced.

Rolling Resistance Index=(Rolling Resistance of Comparative Example1/Rolling Resistance of Example)×100

Static Air Pressure Decreasing Ratio Test

Each trial tire was assembled to a JIS specification rim 15×6JJ, and airwas introduced thereinto at an initial air pressure of 300 kPa. Then,the trial tire was left for 90 days at a room temperature. Then,decreasing ratio of air pressure was calculated after one month. As thenumerical value thereof is smaller, the air pressure is less decreased,which is preferable.

Tire Evaluation Results

Comparative Example 1 is an example strip having no ear portions.Examples 1 and 4 are strips having the cross sectional shape shown inFIG. 6(a). Example 2 is a strip having the cross sectional shape shownin FIG. 5(b). Example 3 is a strip having the cross sectional shapeshown in FIG. 4. The evaluation results of Table 1 reveal that theExamples of the present invention are more excellent than ComparativeExample 1 in the results of air-in, flection crack growth test, rollingresistance index, and static air pressure decreasing ratio test.

INDUSTRIAL APPLICABILITY

The pneumatic tire of the present invention can be used as a pneumatictire for track/bus, a pneumatic tire for heavy vehicle, or the like,besides a pneumatic tire for passenger car.

REFERENCE SIGNS LIST

1: pneumatic tire; 2: tread portion; 3: sidewall portion; 4: beadportion; 5: bead core; 6: carcass ply; 7: belt layer; 8: bead apex; 9:inner liner; 10: strip; 11: strip manufacturing device; 12: sheet; 13:extruder; 14A, 14B: die roller; 15: screw shaft; 16: extrusion port; 17:mouthpiece; 18: free roller; PL: polymer layer stack; PL1: SIBS layer;PL2: SIS layer; PL3: SIB layer.

1. A method for manufacturing a pneumatic tire in which a strip is woundspirally on a cylindrical drum such that a strip main body formsoverlapping portions to form an inner liner, and the inner liner isdisposed on an inner surface of a raw tire, and then vulcanization isperformed wherein, said strip being formed of composite layers of (A) afirst layer made of a styrene-isobutylene-styrene (SIBS) triblockcopolymer, and (B) a second layer comprising: (b1) a layer made of astyrene-isoprene-styrene (SIS) triblock copolymer; and (b2) a layer madeof a styrene-isobutylene (SIB) diblock copolymer containing at least oneadditive selected from the group consisting of stearic acid, zinc oxide,antioxidant, vulcanization accelerator, and sulfur, and disposedadjacently to a carcass ply, said strip further having ear portions onopposite sides of the strip main body, said strip main body having athickness of 0.05 mm to 1.0 mm, and said ear portions having a thicknessthinner than the thickness of said strip main body and a width of 0.5 mmto 5.0 mm.
 2. The method for manufacturing a pneumatic tire according toclaim 1, wherein said strip has a width of 5 mm to 40 mm.
 3. The methodfor manufacturing a pneumatic tire according to claim 1, wherein saidear portions of said strip have a thickness of 0.02 mm to 0.5 mm.
 4. Themethod for manufacturing a pneumatic tire according to claim 1, whereinsaid first layer has a thickness of 0.05 mm to 0.6 mm, and the secondlayer has a thickness of 0.01 mm to 0.3 mm.
 5. The method formanufacturing a pneumatic tire according to claim 1, said strip beingobtained by a manufacturing method including the steps of: (a)coextruding the first layer with the second layer by an extruder havingan extruder main body and an extrusion head to form a sheet having ahorizontally long rectangular cross sectional shape; (b) passing thesheet through a pair of die rollers and transferring a shape of the dierollers on said sheet to form the strip having the ear portions onopposite sides of the main body; and (c) detaching said strip from thedie rollers.